Moose - Mortality


Toxoplasmosis is a disease spread by Toxoplasma gondii, a single-celled organism found as minute oocytes in the feces of cats. It was first diagnosed in moose in 1981 in Montana and subsequently in 23% of Alaskan moose in 1986. Generally this disease is spread through carnivores eating infected animals but is suggested to be picked up by moose eating vegetation near cat scat.

Fascioloidiasis, or liver rot, is caused by the large American liver fluke Fascioloides magna. Scientists are still unsure as to whether or not this parasite is detrimental to moose or not. It does not normally reach maturity inside the moose and therefore cannot reproduce inside of it. The flukes travel around in the liver creating tunnels which leave a decent amount of scar tissue in moose.

Parelaphostrongylosis, or “moose sickness,” is a neurological disease caused by brainworms. It only occurs in the eastern and central parts of North America, not in the West. The parasite lives in the brains of white-tailed deer, is shed through feces, and consumed again by snails which occupy leaves that are in turn consumed by moose. This disease does not affect deer but severely affect moose causing them to act strangely, not be able to stand solidly, and die quickly.

Winter ticks are a problem both in North America and the Eurasian populations of moose. Dermacentor albipictus are found south of 60 degrees North latitude and spend the entire winter on large ungulates. They congregate on the tips of vegetation in large masses. These groups transfer almost as a whole to an ungulate passing by and quickly spread out to begin feeding. The massive amount of ticks make the moose want to scratch off their fur in the hopes of removing the ticks, exposing the white skin underneath. This is how moose inherit the name “ghost moose.” The moose can die either by freezing or by nutrition deficiencies from the ticks literally sucking the moose to death. Estimates of upwards of 30,000 ticks have been found on a single moose and approximately 90% of moose observed in late winter show signs of hair damage due to tick infestations.
Photo Credit:US National Oceanic and Atmospheric Administration


Moose calves have a much lower survival rate than do adult moose due to predation, drowning, vegetative entanglement, and abandonment. However, adults suffer mortality more often to vehicle collisions and falls. Moose are generally very comfortable in human disturbed areas, but that places them very close to highways and roads and subject to more and more collision risk.

Moose and vehicle collisions happen most frequently at dusk and dawn, on straight, flat, stretches of highway, areas with poor visibility (also due to snow), at speeds higher than 50mph, and due to driver inattention. Many techniques have been used to lower these type of incidents including moose crossing signs, clearing of vegetation on the sides of highways to improve horizontal visibility, and local media encouraging caution on days when more moose are sighted near or on roads. In other more specific areas, moose-proof fencing has been used on the sides of highways and has decreased moose and vehicle accidents by 70% overall and 95% in the fenced area.

Drowning is also a concern due to hydroelectric projects and reservoirs. The reservoirs can create very thin ice where moose can fall and drown. Additionally, these structures deplete habitat, concentrate moose while increasing predator vulnerability, and alter dispersal and migration routes including restricting access to traditional calving grounds.